Survival in coronary disease depends on extent of vascular involvement and left ventricular function. Perioperative myocardial infarction can cause immediate death, and decreased long-term survival and function. We have shown that the two basic mechanisms of such injury - occlusion versus reperfusion - can be distinguished not only by histology and the epicardial electrocardiogram, but also by infarct-avid scanning. That is, a reperfusion injury is positive within a few hours while a considerable delay is necessary following occlusion. We will now determine the incidence and mechanism of post-operative injury following aortocoronary bypass surgery.